U.S. Pat. No. 4,928,146, issued to Yamada on May 22, 1990, is illustrative of a number of references which show the development of a series of electrostatic images carried on a photoconductive drum with different color toners at a single development position. A series of four development stations are moved one after another to the development position. Each station develops an image and is replaced by another station as the series of stations is indexed to apply a different color toner to the next image. The series of stations are arranged side-by-side and moved linearly through a position in which the station to be used is aligned with the development position. After or as it is aligned, a cam is rotated to push the entire station toward the development position, generally moving transverse to the motion of the series of stations and moving relative to the other stations.
This general approach has the advantage of using only a single development position for applying four different color toners to electrostatic images. This permits the use of development stations whose size and number would prohibit them being spaced around the periphery of a relatively small photoconductive drum. It, thus, also permits the use of a small photoconductive drum in multicolor imaging. The use of a small drum has many advantages, including reduced expense, reduced size of the apparatus and convenience in cartridge type replacement.
The structure shown in the prior art requires two motions on the part of each development unit. The four units are moved as one, linearly in one direction and the unit opposite the development position is moved relative to the others, transverse to that motion into operative relationship with the photoconductive drum. The second movement requires that the units be mounted so they are movable relative to each other and requires a separate moving mechanism that must be powered sufficiently to move an entire unit.
U.S. Pat. No. 5,182,608 to Kroll et al, issued Jan. 26, 1993, describes a structure which solves some of the problems associated with these prior art structures by providing a movable applicator at the top of each unit which is movable relative to the unit. With a movable applicator the rest of the unit can be fixed with respect to the other units and only the applicators moved for final positioning with respect to the development position. That application shows toner supply chambers positioned longitudinally between the units which supply chambers are either replaceable from above the units or fillable from above the units. Such chambers contain a limited amount of toner and generally would require complete removal of the developing device for replacement of toner. Toner could be supplied in four separate containers, as is generally the case for supplying toner to color electrophotographic apparatus.
U.S. Pat. No. 4,733,269, Kasahara et al, issued Mar. 22, 1988, shows a traditional container for supplying toner to an electrophotographic apparatus. The toner is contained in a plastic bottle having a generally rectangular cross-section with a base having flanges extending outward from opposite sides for inserting in slots in a receiving structure. Once the toner bottle has been positioned over a sump with the flanges held by the slots, a pull tab is pulled, removing a paper seal and opening the bottom, dumping the toner into the sump. The sump does not take all of the toner in the container, and the container, therefore, stays on top of the sump until empty, at which point it is removed and a new toner container positioned. The container, thus, forms a portion of the toner supply system of the apparatus. It extends as far above the sump as the apparatus will permit to hold as much as two liters of toner.
U.S. Pat. No. 4,899,690, Hacknauer etal, issued Feb. 13, 1990, shows a toner bottle similar to that in the Kasahara reference which is designed for a color apparatus which would receive four such bottles side-by-side on stationary sumps.
The packaging for such toner is a significant portion of the cost of supplying the toner. To multiply that packaging cost by four with a four-color image-forming apparatus is undesirable, but it is the present state of the art.